Field of the Invention
The present invention relates to a novel electrical conduit system for encasing and protecting flexible wires or cables, being particularly adapted to adhere to the stricter levels of the electrical code.
Description of the Currently Available Technology
In construction and architectural applications, electrical conduit systems are used to encase and protect flexible delicate or dangerous lines or cables, such as electrical power lines, telephone lines, fiber optic cables, computer network cables, etc. Such electrical conduit systems are used, for example, within the walls of buildings, underground, and for exposed above-ground outdoor applications. Conventional electrical conduit systems consist of individual conduit sections or pieces usually made of rigid material, such as galvanized or stainless steel, PVC, or aluminum, coupled together to form the conduit system, generally referred to as a “conduit run”.
Examples of conventional electrical conduit pieces include the following: straight conduit sections, generally of several feet in length and in varying diameters, with exterior or male threads on each end; nipples, which generally are shorter straight conduit sections of various diameters with exterior or male threads on each end; and elbows, which are generally bent or curved conduit sections also with exterior or male threads on each end. By standard convention, the threads on the ends of the conventional conduit pieces are all right hand threads. Adjacent conduit pieces are connected together by a female coupling having continuous, internal right hand threads.
To construct a conventional electrical conduit system, a first conduit piece, for example a nipple, is secured at one end of the conduit run, usually at the feed end. A female coupling is then screwed onto the outer end of the first conduit piece until seated. Then, a second conduit piece, for example a straight ten-foot section or an elbow, is inserted into the other end of the female coupling and turned to thread it into the female coupling to connect the second conduit piece to the first conduit piece. Additional conduit pieces, connected by additional female couplings, are successively added to form the electrical conduit system. The sections or pieces may be attached to walls or suspended from a ceiling by various known methods.
There are, however, several drawbacks to conventional electrical conduit systems. Although conventional electrical conduit systems are generally acceptable for protecting cables, once formed it becomes difficult to reenter or access an intermediate section of the conduit system. Such reentry typically entails complete disassembly of the conduit system from one end to the point of desired access due to the successive coupling of each conduit piece to form the conduit system. This disassembly is often both costly and labor intensive.
Alternatively, for complex conduit systems, the point of desired access is sometimes gained to intermediate sections by destructive means, generally involving pipe cutting and wire pulling or cutting. This creates the obvious risk of further damaging the wires or cables housed by the conduit system, and also creates a difficulty in having to replace the destroyed conduit piece. This is especially so when the destroyed conduit piece is of a curved nature and there is insufficient room to rotate the replacement conduit piece.
Additionally, when constructing a large, electrical conventional conduit system, the significant weight and size of the conduit pieces require considerable manpower to align the pieces correctly and then to rotate them to screw them into the system. Clearly, the manpower required to align and rotate such large, heavy conduit pieces creates an increased cost of construction.
Furthermore, since the conventional conduit pieces must be rotated during construction of the electrical conduit system, the cables or wires to be protected cannot be pre-positioned inside the disassembled conduit pieces. Rather, after the entire conduit system has been constructed, the cables or wires are typically pulled through the entire conduit system from one end to the other. This pulling may damage the cables or wires and is particularly disadvantageous for fiber optical cables. Since there are generally four or more fiber optical cables in conventional systems, the fiber optic cables are placed in spacers within the conduit system, which can easily become broken, damaged or misaligned during the pulling process.
Therefore, several complex clamping devices have been developed and are commonly employed to alleviate the above-described problems encountered with a conventional electrical conduit system. One such device comprises a split sleeve with an internal threaded region on both sections. The device is bolted over the external threaded region of two components thereby connecting them.
Another device, referred to as an “Erickson” coupling, is comprised of a first sleeve with an internal threaded portion and an internal flange. The first sleeve is slipped over the end of one of the conduit sections and the second sleeve is threaded onto the end of the same conduit. The third sleeve is comprised of an interior threaded portion and an exterior flange and threaded surface. The interior threaded portion of the third sleeve is threaded onto a second conduit piece. The first sleeve is slipped back along the first conduit, fitted over the second sleeve and subsequently rotated or threaded onto the third sleeve. A secure joint is completed as the second sleeve abuts the interior flange of the first sleeve, the first sleeve being threaded against the exterior flange of the third sleeve.
A third method is also employed using the device described in U.S. Pat. No. 4,091,523 (Reicke). The description of the device from the abstract cites: A sleeve having first and second interior surface portions. The first surface portion is threaded and communicates with one open end of the sleeve, the second surface portion is smooth and communicates with the opposite open end of the sleeve. A bore is formed through the sleeve and the second surface portion thereof and a set screw is threaded into the bore. The sleeve is first slipped, and then threaded, onto a first conduit, the conduit being first received by the smooth interior surface and then by the threaded interior surface. The end of the second conduit is then disposed adjacent the sleeve, and the sleeve is screwed back off the first conduit onto the second conduit until the first conduit is received by the smooth interior surface and the second conduit by the threaded interior surface. The set screw is threaded against the first conduit.
These methods using known clamping devices, however, also have several disadvantages. They tend to be expensive to purchase and to install. Additionally, they possess the disadvantage of being bulkier than the original conduit system, thereby requiring a larger free space between parallel or adjacent conduit runs, or a larger free space within confined areas. Further, the aforementioned method devices consist of numerous parts which may become misplaced or lost.
Additionally, several of the above-described devices are of limited use because they are not approved for use in certain types of installations, particularly explosion proof installations, as defined by the various electrical codes. Sufficient thread engagement to cool flame under pressure, and the abutting of conduit section pieces to prevent the current from an electrical short from arcing across the conduit section to the coupling and arcing back across the coupling to the conduit section are required in explosion proof installations. Thus, these devices are useless alternatives when performing or fixing explosion proof installations.
Another device, described at U.S. Pat. No. 4,060,264 (Gajajiva), attempts to solve this dilemma, and provides for a swivel coupling with a resilient seal and a non-centered recess which forces a non-arcing ground. However, while this invention reaches the standard for explosion proof installations in relation to arcing, it fails to assure sufficient thread engagement, required for stricter code installations.
Given the above information, it is clear that a novel electrical conduit piece, and corresponding conduit system, are greatly needed to provide a less burdensome and less expensive means to building and allowing repair access to conduit systems, and which particularly are acceptable under the strictest electrical codes for use in explosion proof installations.